Cobalt (iii) complex amplifier baths in color photographic processes

ABSTRACT

Improved processes are disclosed for providing an image record in a photographic element which comprises a support and at least one layer thereon containing a silver halide emulsion which has associated therewith an image dye-providing color coupler. Generally, the process comprises contacting a photographic element containing a silver halide and an imagewise distribution of metallic silver with a color-developing agent, and then contacting the developed photographic element with an amplifier composition which contains a cobalt(III) complex and an oxidant such as an alkali metal peracid or an alkali metal ferricyanide.

United States Patent [191;

Mowrey et a1.

COBALT (III) COMPLEX AMPLIFIER BATHS IN COLOR PHOTOGRAPHIC PROCESSESInventors: Rowland George Mowrey; Glenn Richard Wilkes, both ofRochester, N.Y.

Eastman Kodak Company, Rochester, N.Y.

Filed: May 21, 1973 Appl. No.: 361,926

Assignee:

[1.8. CI 96/22, 96/3, 96/29 D, 96/55, 96/60 R, 96/66.3

Int. Cl. G03c 7/16, G03c 7/00, G030 5/54, G030 5/32, G03c 5/30 Field ofSearch 96/3, 29 D, 22, 55, 60 R, 96/66.3

References Cited UNITED STATES PATENTS 10/1971 Stephen et'al. 96/60 BF7/1972 Matejec et a1. 96/3 [111 3,841,873 [4 Oct, 15, 1974 3,748,1387/1973 Bissonette 96/66.3 3,762,922 10/1973 Lugosy et al..... 96/60 R3,765,891 10/1973 Travis 96/66.3 3,772,020 Smith 96/60 BF PrimaryExaminer--R0nald H. Smith Assistant Examiner Richard L. SchillingAttorney, Agent, or FirmGerald E. Battist [57] ABSTRACT I Improvedprocesses are disclosed for providing an image record in a photographicelement which comprises a support and at least one layer thereon consuchas an alkali metal peracid or an alkali metal ferricyanide.

17 Claims, No Drawings COBALT (III) COMPLEX AMPLIFIER BATHS IN COLORPHOTOGRAPHIC PROCESSES This invention relates to a process fordeveloping photographic elements which comprise layer units containingimagewise-exposed silver halide having associated therewith aphotographic color coupler. [none aspect, this invention relates toa'process for developing a visible image record in photographic elementswhich comprise color-providing layer units containing a low silvercoverage. In another aspect, this invention relates to a continuousprocess for developing imagewiseexposed photographic elements whichcomprise at least two color-providing layer units.

It is known in the art to process photographic elements comprisingsilver halide emulsions and photographic color couplers wherein saidelement is contacted with an aromatic primary amino silver halidedeveloping agent to form silver and dye. References such as U.S. Pat.No. 2,750,292 by Dippel et al, issued June 12, 1956, and 2,173,739 byWeber issued Sept. 19, 1939, disclose processes for intensifying animageformed by a light-sensitive metal salt by treating the imagewise-exposedelement with a color-developing agent and a photographic color couplerin the presence of developable silver halide orwith a physicaldeveloping agent to form an image. dye in the area of development. Morerecently, British Pat. No. 1,268,126 also discloses a process ofintensifying a silver image by treating, a developed silver image withsolutions containing peroxy compounds and color developers.

However, several of the methods available in the art do not appear to bepractical on a commercial basis due to several problems inherent in thesystem, including instability of the solutions used to intensify theimage record recorded by the light-sensitive metal salt. Where thesilveris bleached and redevelopment takes place with a color developerand a coupler, the bleaching step is quite critical as thedevelopablesilver centers can be lost where bleaching has completelyconverted a silver grain to silver halide. Moreover, solutionscontaining both color-developing agent and color coupler are prone toformation of dye in the bath through aerial oxidation of the developer,etc., causing dye contamination, and also these systems are generallylimited to one-color systems. Where a physical developing agent is usedin combination with a color coupler and a color-developing agent, theprocessing baths are often autocatalytic since the reaction products ofthe redox reaction with the physical developer provide a catalyst formore redox reactions.

Improved processes for developing and amplifying an image recordrecorded in a light-sensitive metal salt are disclosed in Belgian Pat.Nos. 784,471, 784,472 and 784,473, incorporated herein by reference. Inone embodiment, the process disclosed in these patents relates to imageformation in photographic elements comprising color-providing layerunits containing a silver halide emulsion having associated therewitha-color coupler. In the process, the photographic element is contactedwith a photographic color-developing agent and a metal complex, such asa cobalt(III) complex having a coordination numberof 6, until thedesired dye density is obtained. the cobalt complex is apparentlyreduced to cobalt(ll), which is not a catalystfor further redoxreaction, in the presence of silver, and the color developer is oxidizedwhereby it can react with the color coupler in each respective layerunit to form the desired image dye. Certain preferred photographicelements which can be processed by this procedure are described inBissonette, U.S. Ser. No. 256,072 filed May 23, 1972, incorporatedherein by reference.

These patents also disclose a process of producing image dye in animagewise-exposed photographic element having a support and at least onelayer thereon containing a silver halide emulsion having associatedtherewith an image dye-providing color coupler wherein said processcomprises 1) development of said imagewise-exposed photographic elementwith a silver halide developing agent to produce an imagewisedistribution of metallic silver and imbibition of a colordevelopingagent in said photographic element, and then 2) contacting saidphotographic element which contains silver halide and said imagewisedistribution of metallic silver with an amplifier composition whichrepresses substantially additional net silver development, wherein saidamplifier composition contains a cobalt- (lll) metal complex having acoordination number .of 6 and said amplifier composition is maintainedin said photographic element under conditions which reduce cobalt(lll)to cobalt(ll), which in turn oxidizes said color-developing agentwhereby additional image dye is provided'from said image dye-providingcolor coupler and said oxidized color-developing agent.

The amplifier composition acts essentially as a stop bath so far asfurther production of catalytic silver surface is concerned. Further Hand D curve shape changes due to continued development are thereforeminimized. However, in some continuous deep-tank machine developingprocesses, it has been observed that carry-over of color-developingagent from the developer bath to the amplifier bath has caused somesensitometric fluctuations and changes in the H and D curve shape. Thesefluctuations are presumably caused by excess color-developing agent inthe amplifier bath which reduces the diffusion rate of color developerfrom the photographic element. This causes a gradual contrast increase,thereby creating a problem of precise sensitometric control.

This invention relates to an improved process of producing image dye inan imagewise-exposed photographic element having a support and at leastone layer thereon containing a silver halide emulsion having associatedtherewith an image dye-producing color coupler wherein said processcomprises 1) development of said imagewise-exposed photographic elementwith a silver halide developing agent to produce an imagewisedistribution of metallic silver and imbibition of a colordevelopingagent in said photographic element, and then 2) contacting saidphotographic element with an amplifier composition which repressessubstantially additional net silver development, wherein said amplifiercomposition contains a strong oxidizing agent, such as a peracid or aferricyanide, and a cobalt(lll) metal complex having a coordinationnumber of 6.

In one highly preferred embodiment, an image dye is produced in animagewise-exposed photographic element having a support and at least onelayer thereon containing a silver'halide emulsion having associatedtherewith an image dye-providing color coupler. The imagewise-exposedphotographic element is developed in the presence of a silver halidecolor-developing agent. This produces an imagewise distribution ofmetallic silver and imbibition of a color-developing agent in thephotographic element. The developed photographic element which containssilver halide and the imagewis'e distribution of metallic silver is thencontacted with an amplifier composition which represses substantiallyadditional net silver development. A strong oxidant is added to theamplifier during processing to oxidize selectively any excess developingagent which may have been carried into the amplifier bath.

Generally, good results have been obtained when the strong oxidant usedin the amplifier bath is an alkali metal salt of a peracid or of aferricyanide', and preferably when it is an alkali metal salt of aperacid. Typical useful ferricyanides include potassium ferricyanide andthe like. Typical useful peracids include potassium persulfate,potassium perbromate, potassium permanganate, potassium perchlorate,sodium persulfate, sodium perbromate, sodium permanganate and the like.While the oxidizing agent can comprise any of the alkali metal ions suchas sodium, potassium, lithium and the like, it preferably comprises apotassium ion, i.e., the potassium salt of the peracid or offerracyanide.

the photographic elements processed as above can, of course, bebleached, fixed, and washed, etc., in the normal manner after contactwith the amplifier. Generally, this process also provides highlyimproved stability of development compositions and amplifyingcompositions and is especially suitedto continuous processing of colorphotographic elements. The process is especially advantageous inprocessing multicolor photographic elements' since stability inprocessing solutions is highly improved, allowing reproducible resultsover long periods of operating time.

In one preferred embodiment, the amplifier solution contains asufficient quantity of a development restrainer or combination ofdevelopment restrainers to repress substantially any further net silverdevelopment. The development restrainers may be watersoluble bromidecompounds such as KBr, etc., or heter-' ocyclic compounds such astetrazoles, azaindines and triazoles which are free from mercapto orionic iodide groups. Development restrainers as a class of compounds areknown in the art, as mentioned in U.S. Pat. No. 3,458,317. Developmentrestrainers which have ionic iodide groups or mercapto groups appear toretard the catalytic effect of silver. Typical preferred de velopmentrestrainers include high levels of KBr such as 2 to 40 g./l., methylbenzotriazole, benzotriazole, B-methyl-1,3-benzothiazolium bromide,nitrobenzimidazole, decamethylene bis(benzothiazolium bromide) and thelike. Other useful organic development restrainers include the sodiumsalt of 4 hydroxy-tS-methyl-l,3,3a,7-tetrazaindene, the sodium salt of4-hydroxy-6-methyl-2-methylmercaptol,3,3a,7-tetrazaindene, 4,5-dihydro-l,4-diphenyl-3,5- phenylamino-l ,2,4-triazole and the like. Theheterocyclic development restrainers are generally incorporated in theamplifier at concentrations of 0.01 to 2.0 g./l. In certain embodiments,the heterocyclic groups containing sulfur substitution can be used asdevelopment restrainers where the compound as used in the amplifierremains in its thione form rather than in the thiol or mercapto forms.In highly preferred embodiments, a combination of an alkali metalbromide and an organic development restrainer are present in theamplifier composition.

The amplifying baths of this invention preferably contain only lowamounts or are substantially free from silver halide solvents. lf highamounts of solvents are present, there is very little noticeableamplification effect in the bath. Therefore, the amplifying bathsgenerally comprise less than 30 percent by weight of the amount of asilver halide solvent which would be necessary to fix a silver halideemulsion. The fixing processes are well-known in the art, for example.as disclosed in U.S. Pat. No. 3,615,508.

As used herein, the terms photographic color coupler and imagedye-providing color coupler" include any compound which reacts (orcouples) with the oxi' dation products of primary aromatic aminodeveloping agenton photographic development to form an image dye, andare preferably nondiffusible in a hydrophilic colloid binder, useful forphotographic silver halide, and also those couplers which provide usefulimage dyes when reacted with oxidized primary aromatic amino developingagents such as by a coupler-release mechanism. The couplers can formdiffusible or nondiffusible dyes. Typical useful color couplers includephenolic 5-pyrazolone and open-chain ketomethylene couplers. Specificcyan, magenta and, yellow dyeforming couplers which can be employed inthe practice of this invention are described in U.S. Pat. No. 3,046,129,column 15, line 45, through column 18, line 51, which disclosure isincorporated herein by reference. Such color couplers can be dispersedin any convenient manner, such as by using the solvents and techniquesdescribed by U.S. Pat. Nos. 2,322,027 or 1,801,171. When couplersolvents are employed, the most useful weight ratios of color coupler tocoupler solvent range from about 1:3 to 1:01. Useful couplers includeFischer-type incorporated couplers such as those described in U.S. Pat.No. 1,055,155 and particularly nondiffusible Fischer-type couplerscontaining branch carbon chains, e.g., those referred to in thereferences cited in U.S. Pat. No. 2,376,679, column 2, lines 50-60.Particularly useful in the practice of this invention are thenondiffusible color couplers which form nondiffusible dyes.

In certain preferred embodiments, the incorporated couplers in the layerunits of this invention are waterinsoluble color couplers which areincorporated in a coupler solvent which is preferably a moderately polarsolvent. Typical useful solvents include tri-o-cresyl phosphate,di-n-butyl phthalate, diethyl lauramide, 2,4- diaryphenol, liquid dyestabilizers as described in an article entitled improved PhotographicDye Image Stabilizer-Solvent, Product Licensing Index, Vol. 83, March,1971, and the like. The coupler solvents in the elements appear to aidthe imbibition of color developer where it is carried into an amplifierbath via the element.

The photographic elements processed in accordance with this inventiongenerally comprise a light-sensitive silver halide emulsion wherein thehalide is generally less than 6 mole percent iodide and preferably lessthan 3 percent iodide and, in some highly preferred embodiments, is lessthan 0.25 percent iodide. lf iodide is near the surface of the emulsiongrains, it can build up in the solutions at a high level duringdevelopment and amplitication and affect dye production in theamplification step. Therefore, high amounts of iodide in the emulsionare generally avoided, especially when the element is to be processed ina continuous-process deep-tank apparatus where seasoning can occur. I

The term nondiffusible used herein as applied to couplers and productsderived from couplers has the meaning commonly applied to the term incolor photography and denotes materails which for all practical purposesdo not migrate or wander through photographic hydrophilic colloidlayers, such as gelatin, particularly during processing in aqueousalkaline solutions. The same meaning is attached to the term immobile."The terms diffusible" and mobile have the converse meaning.

In certain embodiments, the photographic elements processed inaccordance with this invention comprise a support having thereon imagedye-providing layers units. A multicolor photographic element comprisesat least two of said image dye-providing layer units, each of whichrecords light primarily in different regions of the light spectrum. Thelayer unit comprises a lightsensitive silver salt, which is generallyspectrally sensitized to a specific region of the light spectrum, andhas associated therewith a photographic color coupler. In certainembodiments, the color-providing layer units are effectively isolatedfrom other layer units by barrier layers, spacer layers, layerscontaining scavengers for oxidized developer and the like to prevent anysubstantial color contamination between the image dyeproviding layerunits- The effective isolation of the layer units is known in the artand is utilized to prevent color contamination in many commercial colorproducts.

the photographic elements prepared in accordance with this inventionpreferably comprise asupport having thereon at least one imagedye-providing layer unit, and preferably at least two imagedye-providing layer units, containing a light-sensitive silver salt,preferably silver halide, having associated therewith a stoichiometricexcess of coupler of at least 40 percent and preferably at least 70percent. The equivalency of color couplers is known in the art; forexample, the 4- equi'valent couplers require 4 moles of oxidized colordeveloper, which in turn require development of 4 moles of silver, toproduce 1 mole of dye. Thus, for a stoichiometric reaction'with silverhalide, l-equivalent weight of this coupler will be 0.25 mole. Inaccordance with this embodiment, the color image-providing unitcomprises at least a 40 percent excess of the equivalent weight of imagedye-providing color coupler required to react with the silver andpreferably a 70 percent excess of said coupler based on effectivesilver. In certain highly preferred embodiments, the photographic colorcouplers are employed in the image dye-providing layer units at aconcentration of at least 3 times, such as from 3 to times, the weightof the silver in the silver halide emulsion, or at a stoichiometricexcess of at least 1 10 percent based on effective silver in saidlayerunit. Advantageously, the coupler is present in an amount sufficient togive a density of at least 1.7 and preferably at least 2.0 when coatedon a paper support, and preferably at least 3.0 when coated on atransparent film support. Generally, the coupler is present in saidlayer units in at least 1 X 10 moles/ft. Preferably, the differencebetween the maximum density and the minimum density (which can compriseunbleached silver) is at least 0.6 and preferably at least 1.0.Preferably, the photographic elements prepared in accordance with thisinvention are those described in the above Bissonette application U.S.Ser. No. 256,072.

Advantageously, the photographic color couplers utilized are selected sothat they will give a good neutral. Preferably, the cyan dye formed hasits major absorption between about 600 and 700 nm., the magenta dye hasits major absorption between about 500 and 600 nm., and the yellow dyehas its major absorption between about 400 and 500 nm. I

Generally, each of the color-providing layer units of the photographicelements contains a light-sensitive silver halide. In one preferredembodiment, the colorproviding layer units comprise a silver salt at aconcentration of up to 30 mg. silver/ft? However, while the silverhalide is preferably present at concentrations based on silver of lessthan 30 mg./ft. it is possible to coat emulsions at higher silvercoverages within this embodiment, as long as no more than 30 mg./ft. ofsilver develops; for example, such emulsions may contain silver halidegrains which are relatively lightinsensitive, or may contain developerrestrainers such as development inhibitor-releasing couplers, and stillprovide a photographic element which is advantageously used in thevarious processes as described herein to produce improved image records.In some instances, relatively light-insensitive silver halide grains ordevelopment restrainers are desirable to enable one to obtain moreuniform coating coverage with less precise coating equipment, as well asfor other reasons. Thus, highly preferred photographic elementsprocessed'according to this invention contain at least twocolor-providing layer units, each containing a silver halide emulsion,defined in terms of effective coverage and developability as one which,when it is fully exposed and processed for about 1 min. at F. in thecolor developer as described in Example 1, will provide less than 30 mg.of metallic silver/ft. and preferably less than 15 mg./ft. It isunderstood that the term effective silver refers to that amount ofsilver which is produced in this test and that ratios of coupler tosilver are based on effective silver which is produced by this type ofdevelopment when so specified herein. In most instances, the quantity ofeffective silver as silver halide in the undeveloped, unexposedphotographic element will be quite similar to quantity of total silverpresent as silver halide. The fully exposed layer containing silverhalide emulsion is one which is exposed to Dmax, as is well-known in theart, for example, by exposure to a 500-watt, 3,000 K. lamp for about 10sec. (total exposure at the film plane 11.3 X 10 ergs/cmF.

The photographic elements processed in accordance with this inventiongenerally can contain negative silver halide emulsions, direct-positivesilver halide emulsions, silver halide emulsions designed for processingin reversal processes and the like. It is understood, of course, thatwith negative emulsions the catalytic metallic silver development willbe in. the exposed areas, whereas with direct-positive emulsions thecatalytic metallic silver will be formed in the unexposed areas.

' The amplifier compositions of this invention include a cobalt(lll)metal complex. Such complexes feature a molecule having a cobalt atom orion. This cobalt atom or ion is surrounded by groups of atoms, ions orother molecules, which are generically referred to as ligands. Thecobalt atoms or ion in the center of these comreferred to by Americanchemists as inert and by European chemists as robust. Particularlyuseful are complexes of a cobalt ion with a ligand which, when a testsample thereof is dissolved at 0.1 molar concentration at 20 C. in aninert solvent solution also containing 0.1 molar concentration of atagged ligand of the same species which is uncoordinated, exhibitsessentially no exchange of uncoordinated and coordinated ligands for atleast 1 min., and preferably for at least several hours such as up to 5hr. or more. This test is advantageously conducted under the pHconditions which will be utilized in the practice of the invention. Insilver halide photography, this generally will be a pH of over about 8.Many cobalt metal complexes useful in this invention show essentially noexchange of uncoordinated and coordinated ligands for several days. Thedefinition of inert metal complexes and the method of measuring ligandexchange using metal radioactive isotopes to tag ligands is well-knownin the art: see, for example, Taube, Chem. Rev.,.Vol. 50, p. 69 (1952),and Basolo and Pearson, Mechanisms-f Inorganic Reaction, A Study ofMetal Complexes and Solutions, 2nd Edition, 1967, published-by JohnWiley and Sons, .p. 141. Further details on measurement of ligandexchange appear in articles by Adamson et al, J. Am. Chem 500., Vol. 73,p. 4,789 (1952). The inert metal complexes should be contrasted withlabile complexes which, when tested by the method described above, havea reaction half-life generally less than 1 min. Metal chelates are aspecial type of metal complex in which the same ligand (or moleculelisattached to the central metal ion at two or more different points. Themetal chelates generally exhibit somewhat slower ligand exchange thannonchelated complexes. Labiletype chelates may have a half-life ofseveral seconds or perhaps slightly longer. Generally, the oxidizingagents employed are not reduced to a zero valent metal during the redoxreaction of the invention.

A wide variety of ligands can be used with a metal ion to form suitablecobalt complexes. Nearly all Lewis bases (i.e., substances having anunshared pair of electrons) can be ligands in cobalt complexes. Sometypical useful ligands include the halides, e.g., chloride, bro mide,fluoride, nitrite, water, amino, etc., as well as such common ligands asthose referred to on p. 44 of Basolo et al, supra. The lability of acomplex is influenced by the nature of the ligands selected in formingsaid complex.

Particularly useful cobalt complexes have a coordination number of 6 andhave a ligand selected from the group consisting of ethylenediamine(en),propylenediamine(tn), diethylenetriamine(dien),triethylenetetraamineflrieii), amrnine(Nl-la). nitrate, nitrite, azide,chloride, thiocyanate, isothiocyanate, water and carbonate. thepreferred cobalt complexes comprise l )at leastZ'ethylenediamine ligandsor 2) at least amine ligands or 3) l triethylenetetraamine ligand.Especially useful are the cobalt hcxamminc salts (e.g.-, the chloride,bromide, sulfite. sulfate, perchlorate, nitrite and acetate salts). Someother specific highly useful cobalt complexes include those having oneof the following formulas: [Co(NH l-l O)]X,

[Co(tn)(en) ]X, wherein X represents one or more anions determined bythe charge neutralization on rule.

With many complexes, such as cobalt hexammine, the anions selected cansubstantially affect the reducibility of the complex. The following ionsare listed in the order of those which give increasing stability tocobalt hexammine complexes: bromide, chloride, nitrite, perchlorate,acetate, carbonate, sulfite and sulfate. Other ions will also affect thereducibility of the complex. These ions should therefore be chosen toprovide complexes exhibiting the desired degree of reducibility. Someother useful anions include chloride, nitrate, thiocyanate, dithionateand hydroxide. Neutral complexes such as [Co(dienXSCNhOl-l] are useful,but positively charged complexes are generally preferred.

Where highly active complexes are selected for use in the amplifierbath, such as [CO(NH3)5H2O]X3 or [Co(Nl-l Cl]X either as the sole cobaltcomplex or as one to be used in combination with another cobalt complex,the effects of the buildup of color developer appear to be minimized.However, the use of alkali metal peracids or ferricyanide which are veryeffective for controlling buildup of color developer in amplifier bathscontaining the less active cobalt complexes also show some improvementseven when the highly active cobalt complexes are used.

Numerous color-developing agents can be imbibed in i the photographicelement in accordance with the present invention. The color-developingagents utilized herein undergo redox reaction with the oxidizing agentat a catalytic surface. Especially preferred colordeveloping agents arethose which reduce silver halide to metallic silver, such as those whichare capable of developing imagewise-exposed light-sensitive photographicsilver halide. Typical preferred colordeveloping agents are aromaticprimary amino colordeveloping agents-such as p-aminophenols, which formparticularly stable redox combinations with certain complexes, e.g.,[Co(en Cl or p-phenylenediamines. Useful color-developing agents include3-acetamido-4- amino-N,N-diethylaniline, p-amino-N-ethyl-N-Bhydroxyethylaniline sulfate, N,N-diethyl-pphenylenediamine,2-amino-5-diethylaminotoluene,N-ethyl-N-B-methanesulfonamidoethyl-3-methyl-4- aminoaniline,4-amino-N-ethyl-3-methylN-(B-sulfoethyl)aniline,4-amino-N-butyl-N-a-sulfobutylaniline,4-arnino'N,N-diethyl-3-n-propylaniline hydrochloride and the like. SeeBent et al, JACS, Vol. 73, pp. 3,l00-3.125 (i951), and Mees and James,The Theory of the Photographic Process, 3rd Edition, l966, published byMacMillan Co., New York, pp. 278-31 1, for further typical, usefuldeveloping agents. It will be appreciated that many of the subjectcolor-developing tnary amino color-developing agents which provide goodresultsin the process of this invention are 4-amino-N,N-diethylanilinehydrochloride, 4-amino-3- methyl-N,N-diethylaniline hydrochloride,4-amino-3- 9 methyl-N-ethyl-N-B-(methanesulfonamido)ethylaniline sulfatehydrate, 4-amino-3-methyl-N-ethyl-N-B- hydroxyethylaniline sulfate,4-amino-3-dimethylamino- N,N-diethylaniline' sulfate hydrate, 4-amino-3-methoxy-N-ethyl-N-B hydroxyethylaniline hydrochloride,4-amino-N-ethyl-N-(Z-methoxyethyl)-m-toluidine di-paratoluene sulfonateand 4-amino-3-B- (methanesulfonamido)- ethyl-N,N-diethylanilinedihydrochloride.

The term color developer as used herein generally refers to those silverhalide developing agents which after oxidation couple with aphotographic color coupler to form an addition compound such as an imagedye. Generally, these compounds contain a primary amino group (-NH andthey are perferably aromatic primary amino compounds where the primaryamino group is a substituent on the aromatic ring.

The term black-and-white silver halide developers" as referred to hereingenerally refers to those developers which do not couple withphotographic color couplers to form useful image dyes. Theblack-and-white silver halide developers can be effectively used in someinstances in the formation or development of the metallic silver in thephotographic element. Typical useful developers of this type includehydroquinones, catechols, 3-pyrazolidones such as l-phenyl-3-pyrazolidone, l-phenyl-4,4 dimethyl-3 pyrazolidone,l-phenyl-4-methyl-3-pyrazolidone and the like, l-, dor isoascorbic acid,reductones, N-methyl-paminophenols, and the like.

The amplifier bath can generally comprise any liquid as a carriermedium, but the liquid is preferably predominantly water. The bathgenerally comprises from about 0.2 to about 20 g./l. of the transitionmetal-ion complex which preferably is maintained at between about 1 toabout g./l. However, generally higher concentrations of cobalt complexescan be used in preferred amplifier baths of this invention withoutadverse sensitometric effects, compared with color-developing solutionswhich contain the cobalt complexes which contain sufficientcolor-developing agent to develop substantial amounts of silver haliderapidly.

The alkali metal peracid or alkali metal ferricyanide are generallyadded to the amplifier during processing in a concentration sufficientto maintain the colordeveloper concentration at a level of below 0.5g./l., and preferably at a level of below 0.05 g./l. Since the rate ofcolor-developer buildup will depend on the type of element beingprocessed, the size of the equipment, etc., the rate of addition of thestrong oxidant is determined for each particular situation. While excessstrong oxidant can be used, it is generally not preferred to use excessstrong oxidant since the efficiency of color formation in the processedelement could be lowered, adverse interaction could occur, etc.

The amplifier bath also generally contains a solubilizer for theoxidized color developer or soluble competing couplers which formcolorless dyes with the oxidized color developer. Suitable solublecouplers include those described by Puschel, U.S. pat. No. 3,028,238,and the like. Suitable solubilizers include sodium sulfite and the like.Generally, when solubilizers such as sulfites are used in the amplifierbath, they are added to maintain the sulfite level at at least 0.5 g./l.and preferably at least 2.0 g./l. When either the solubilizers or thecompeting couplers are used. it is desirable to have at least astoichiometric amount present based on the oxidized color developer orthe strong oxidant, and preferably at least a 20 percent excess.especially when excess oxidant is present in the amplificr.

The amplifier bath generally contains a development restrainer andpreferably contains enough development restrainer to repress any furthersilver formation. Thus, the sensitometric changes associated with thedevelopment of silver are avoided. Moreover, this feature enables one touse various grain sizes in various layers of a multicolor element toobtain a balanced photographic element and simultaneously to providesubstantially uniform color formation in each layer, whereby balancedcolor can be obtained at several densities by inspection.

The organic development restrainers (i.e., other than the inorganicdevelopment restrainers such as the alkali metal bromides) mentionedpreviously can be used in the bath in combination with the inorganicdevelopment restrainers or alone, but are preferably used in combinationwith alkali metal bromides. Generally, the organic developmentrestrainers are used in concentrations of from 0 to 2 g. and preferablyfrom 0.01 to l g./l.

The amplifier bath is generally operated in a pH range of from 6m 14 andpreferably at pH ranges of 8 to 12. 4

The amplifying baths contain only small amounts of or are substantiallyfree from silver halide solvents such as sodium thiosulfate,thiocyanates, thioethers and the like. While bromide ions are oftendesirable in small amounts of about 2 to 40'g./l. of amplifying solutionto repress development, high concentrations such as above 200' g./l.could function to bleach silver halide layers and, likewise, defeat theprimary amplification step. In certain embodiments, it is also desirableto maintain the ammonia in the amplifier at less than 10 g./l.- sincehigh ammonia concentrations can act as a silver halide solvent, thusallowing bleaching of the silver image.

The term silver halide solvents generally refers to compounds andconcentration levels of those compounds which, when employed in anaqueous solution (60C.), are capable of dissolving more than 10 timesthe amount (by weight) of silver chloride than that which can bedissolved by water at 60 C.

The concentration of a solvent necessary to fix a silver halide layer isunderstood to mean that concentration of solvent in a liquid bath whichwill remove substantially all silver bromide from a photographic elementcontaining a single silver bromide gelatin emulsion layer coated at 30mg. silver/ft. in 1% min. at 105 F. maintained at a pH range within40-120.

The amplifier bath can be operated over a wide range of temperaturesdepending on the efiect desired. Generally, the amplifier bath is muchmore stable than amplifier baths previously used and, therefore, ispreferably used in processes where it is operated at temperatures aboveF. and more preferably above F. to decrease the residence time of aphotographic element in the bath, thus speeding up the process. Theamplifier baths of this invention which are used continuously for 1 weekat F. provide substantially the same development properties as a freshamplifier bath.

The developing baths and amplifier solutions of this inventionpreferably contain a coupling accelerator which can be an alcohol,including aromatic alcohols such as benzyl alcohol, which appears toincrease dye yields. Preferably, the alcohol is used in the respectivebaths at a concentration of up to 40 g./l. and preferably from about 2g. to 20 g./l. Coupling accelerators are known in the art, forexample,the alcohols disclosed in U.S. Pat. Nos. 2,304,925, 2,950,920and the like.

in certain instances, alcohols such as benzyloxyethanol, cyclohexanol,pentyl alcohol, phenoxyethyl alcohol, phenylethyl alcohol and the likeprovide better thermal stability in the amplifier than benzyl alcoholand still aid in increasing dye yields.

Preferably, the process is carried out in a unidirectional processingequipment where the element leaves a bath in the same relative directionwith respect to the plane of the element as it eneters the bath. Incertain preferred embodiments, a continuous web of the photographic'material is processed in unidirectional continuous-processing equipment.

The invention can be further illustrated by the following examples.

EXAMPLE l-A To serve as one control, a photographic element is preparedby coating the following layers in order on a paper support:

1. layer containing a blue-sensitive silver halide emulsion (1.2 micronsmean grain size) at 16 mg./ft. based on silver, gelatin at 122 mg./ft.and the yellow image dye-providing coupler a-pivalyl-4-(4- benzylo-xyphenylsulfonyl )-phenoxy-2-chloro-5 a-(2,4-di-tert-amylphenoxy)butyramido] acetanilide at 60 mgJft. dissolvedin di-n-butyl phthalate coupler solvent at 15 mg./ft. I

2. gelatin interlayer at 100 mg./ft. and the scavenger foroxidized-developer di-tert-octyl hydroquinone at 5 mg./ft.

. 3. layer containing a green-sensitive silver halide emulsion (0.3micron mean grain size) at l mg./ft.* based on silver gelatin at 132mg./ft. and the magenta dye-providing color coupler l-(2,4,6-trichlorophenyl)-3-{5-[a-(3-tert-butyl-4-hydroxyphenoxy)tetradecaneamido]-2- chloroanilino} --pyrazolone, atrng./ft.= dissolved in tri-cresyl phosphate coupler solvent at 12.5mg/ftF;

4. gelatin interlayer at 160 mg./ft. and di-tert-octyl hydroquinone. at4.5 mg./ft.

5. layer containing a red-sensitive silver halide emulsion (0.3 .micronmean grain size) at 6 mg./ft. based on silver gelatin at 90 mg./ft. andthe cyan dye image-providing coupler2-[a-(2,4-di-tertamylphenoxy)butyramido]-4,6-dichloro-5- methylphenol atrug/ft. dissolved in di-n-butyl phthalate coupler solvent at 17.5mg./ft.

6. gelatin overlayer at 100 mg./ft. of gelatin.

Samples of the coating are sensitometrocally exposed to a multicolorgraduated-density test object and then processed in the followingsequence:

color-develop i 0 min (40C amplify l5 min (40 C bleach-fix 1.0 min (40 Cl wash 1 5 min ('26 L l dry The respective baths have the followingcompositions:

Color Developer A benzyl alcohol l5 ml. K 4' g. KBr 0.4 g. hydroxylaminesulfate 2 g. 4umino-N-ethyl-N-(Z-mcthoxyelhyhm- 7.5 g.

toluidine di-paratolucne sullonatc K- -CO 30 g. diaminopropzmoltetraacetic acid 5 g. water to 1 liter pH um Amplifier A [CO(NH:I)6]C[ 1Ill g. KBr 2 g. benzyl alcohol l5 ml. K,CO;, 7.5 g. K 80 2.0 g.diaminopropanol tctraacetic acid 10.0 g. water to 1 liter; pH l0.l

Bleach-Fix diaminopropanol tetraacetic acid 3 g. acetic acid 20 ml. 60%(Ni-10 5 0;, l50 ml. Na SO l5 g. [Co(NH;,)6lCl,, 3 g. water to 1 literpH 4.5

EXAMPLE lB A sample (Element 1) of the photographic element of Examplel-A is processed as in Example l-A wherein Amplifier A is replaced withAmplifier B which contains 700 ml. of Amplifier A and 300 ml. of ColorDeveloper A which simulates the carry-over of color-developer solutioncarried over during a continuous deep tank-processing step.

EXAMPLE l-C Additional samples of the photographic element of Examplel-A are processed as in Example 1-A using Amplifier B with the additionof the ingredients as specified as follows:

Element 2 Amplifier B 5 ml. ammonium hydroxide Element 3 Amplifier B 0.2g./l. ol potassium persulfate Element 4 Amplifier B 0.4 gjl. ofpotassium persulfate Element 5 Amplifier B 0.8 g./l. of potassiumpersulfate Element 6 Amplifier B 1.6 g./l. of potassium persulfateElement 7 Amplifier B 3.2 gJl. of potassium persulfate EXAMPLE 2 Amultilayer photographic element is prepared by coating the followinglayers in order, with the ingredients being listed in mg./ft.

' 1. paper support;

2. layer containing blue-sensitive silver halide emulsion at 16 lug/ft.based on silver, gelatin at 150, and the yellow image dye-formingcoupler a-pivalyl-4-( 4-benzyloxyphenylsulfo nyl )phenoxy-2- 13chloro--[a-(2,4-di-t'ert-amylphenoxy)- butyramido1aceta'nilide at 75;

3. layer-containing gelatin'at 80; Y 4. layer containing agreen-sensitive silver halid emulsion at at mg./ft. based on silver,gelatin at 5 60, and the magenta image dye-forming color coupler l-(2,4,6-tric hlorophenyl) 3-{5-[-( 3-tert-4-hydroxyphenoxy)tetradecaneamid'o} chloroanilino}-5-pyrazolone at 30;

Additional samples of the above photographic element are processed bythe above procedure wherein Amplifier C additionally contains 5 g./l.ofthe developing agent 4-amino-N-ethyl-N-(2-n1ethoxyethyl-mtoluidinedi-paratoluene sulfonate and also K 5 0 and Na So as indicated in thefollowing table.

Similar improvements are also obtained when potassium ferricyanide,potassium perbromate, potassium permanganate or potassium perchlorateare used in 5. layer containing gelatin at 231; 10 Amplifier-C in placeof the potassium persulfate.

Table l K2520 N so. Dmin Contrast (y) Element g./l. g./l. R G B R G B 8(control-Amplifier C) 0.15 0.14 0.22 2.5 2,9 2.6 9 0.21 0.22 0.30 3.63.8 3.3 10 2.43 0.23 0.19 0.27 2.4 3.0 2.8 11 2.43 2.0 0.14 0.16 0.242.5 2.9 2.6 12 2.43 4.0 0.20 0.17 0.27 2.6 2.8 2.4 13 2.43 6.0 0.15 0.170.24 2.3 2.7 2.3 14 2.43 8.0 0.16 0.16 0.25 I 2.4 2.6 2.3 15 2.43 10.00.18 0.18 0.26 2.6 2.8 2.2

6. .layer containing a red-sensitive silver halide emul- EXAMPLE 3 sionat 6 mg./ft. based on silver, gelatin at 65, and the cyan dyeimage-forming coupler2-[ot-(2,4,-ditert-amylphenoxy)butyramido]-4,6-dichloro-5- methylphenolat 35;

7. layer containing gelatin at 100.

The photographic element is exposed through a graduated-dens1ty test obect and processed 1n the following sequence at 40 C.:

color-develop 1.0 min amplify l.5 min bleach-fix 1.0 min wash 1.5 mindry The processing baths have the following composition:

Color Developer benzyl alcohol l5 ml. K 50 H 4 g. KBr 0.4 g.hydroxylamine sulfate 2 g. 4-amino-N-ethyl-N-(2-methoxyethyl-m- 7.5 g.

toluidine di-paratoluene sulfonate K CQ 30 g. diaminopropanoltetraacetic acid 5 g. water to 1 liter pH 10.1

Amplifier C benzyl alcohol l5 ml. [Co(NH;,)6]Cl l0 g. KBr 2 g. K- CO 7.5g. K 80 2.0 g. diaminopropanol tetraacetic acid 10.0 g.S-methylbenzotriazole 300 mg. water to 1 liter pH 10.1

Bleach-Fix diaminopropanol tetraacetic acid 3 g. acetic acid 20 ml.(Ni-M 8 0, 150 ml. 60 Na SO 15 g. lCo(NH )6]Cl; 3 g. water to 1 liter pH4.5

The processed sample (control) is sensitometrically evaluated byrecording the H and D curves of the developed yellow, magenta and cyandye images. the re- I sults are shown in Table l.

Additional samples of the-photographic element of Example 2 areprocessed as in that example, except the following amplifier baths areused.

Element Amplifier The processed samples are sensitometrically evaluated.Element 18 has substantially the same H and D curve shape as Element 17,except that Element 18 has a higher Dmin than either Elements 17 or 16.

As can be observed from the foregoing examples, the changes in Dmin,Dmax and Contrast of continuously processed photographic elements areminimized by the addition to the bath of certain alkali metal peracidsor alkali metal ferricyanides. These examples also show that otherstrong oxidants such as hydrogen peroxide do not minimize the changesbrought about by excess color developers presence in the amplifier bath.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:

1. In a process of developing an imagewise-exposed photographic elementcomprising a support and at least one image dye-providing layer unitthereon which contains a light-sensitive silver halide emulsion havingassociated therewith a color coupler, which process includes developmentof the imagewiseexposed silver halide emulsion to provide an imagewisedistribution of metallic silver and imbibition of a color-developingagent in said photographic element, and then contacting saidphotographic element with an amplifier composition which repressessubstantially additional net silver development, wherein said amplifiersolution contains a cobalt([ll) metal complex having a coordinationnumber of 6 and said amplifier solution is maintained in contact withsaid photographic element under conditions which reduce said cobalt(lll)to cobalt(ll) and in turn oxidize said color-developing agent to providean increase in dye density with dye produced from said coupler in theareas corresponding to the imagewise distribution of said metallicsilver, the improvement comprising including in said amplifiercomposition a compound which isan alkali metal salt of a peracid or offerricyanide.

2. A process according to claim 1 wherein said amplifier bath contains asufficient quantity of development restrainer to repress substantiallyany further net silver development.

3. A process according to claim 1 wherein said colordeveloping agentimbibed in said photographic element is an aromatic primary aminocompound.

4. A process according to claim 1 wherein said development of theimagewise-exposed silver halide emulsion is carried out in a liquidwhich is substantially free from cobalt (lll) metal complex salts.

5. A process according to'claim 1 wherein said amplitier bath issubstantially free from silver halide solvents or contains less thanpercent by weight of the silver halide solvent which would be necessaryto fix a silver halide emulsion.

I 6. A process according to claim 1 wherein the compound is potassiumpersulfate.

7. A process according to claim 1 wherein said compound is added to saidamplifier to maintain the concentration of color-developing agent below0.5 g./l.

8. A process according to claim 1 wherein said photographic element is amulticolor photographic element comprising at least two color-providinglayer units, each of which contains a silver halide emulsion havingassociated therewith a photographic color coupler in at least a percentstoichiometric excess based on silver. 9. A process according to claim 1wherein said photographic element is a photographic element comprisingat least one image dye-providing layer unit which contains a silverhalide emulsion having associated therewith a water-insoluble imagedye-providing coupler dissolved in a coupler solvent wherein saidcoupler is present in at least a 40 percent stoichiometric excess basedon effective silver.

10. A process according to claim 8 wherein each of 0.01 to about 2 g./l.ofa benzotriazole and from 2 g. to

about 40 g./l. of an alkali metal bromide.

14. A process according to claim 1 wherein said amplifier bath containsfrom about 2 g. to about 40 g./l. of an alkali metal bromide.

15. A process according to claim 1 wherein said cobalt(lll) metalcomplex is a cobalt hexammine salt.

16. A process according to claim 1 wherein said am plifier contains atleast 0.5 g./l. of a sulfite compound.

17. A process according to claim 1 wherein said compound is a peracid.

1. IN A PROCESS OF DEVELOPING AN IMAGEWISE-EXPOSED PHOTORAPHIC ELEMENTCOMPRISING A SUPPORT AND AT LEAST ONE IMAGE DYE-PROVIDING LAYER UNTITHEREON WHICH CONTAINS A LIGHT SENSTIVE SILVER HALIDE EMULSION HAVINGASSOCIATED THEREWITH A COLOR COUPLER, WHICH PROCESS INCLUDES DEVELOPMENTOF THE IMAGEWISE-EXPOSED SILVER HALIDE EMULSION TO PROVIDE AN IMAGEWISEDISTRIBUTION OF METALLIC SILVER AND IMBIBITION OF A COLOR-DEVELOPINGAGENT IN SAID PHOTOGRAPHIC ELEMENT, AND THEN CONTACTING SAIDPHOTOGRAPHIC EMEMENT WITH AN AMPLIFIER COMPOSITION WHICH REPRESSESSUBSTANTIALLY ADDITIONAL NET SILVER DEVELOPMENT, WHEREIN SAID AMPLIFIERSOLUTION CONTAINS A COBALT(III) METAL COMPLEX HAVING A COORDINATIONNUMBER OF 6 AND SAID AMPLIFIER SOLUTION IS MAINTAINED IN CONTACT WITHSAID PHOTOGRAPHIC ELEMENT UNDER CONDITIONS WHICH REDUCE SAID COBALT(III)TO COBALT(II) AND IN TURN OXIDIZE SAID COLORDEVELOPING AGENT TO PROVIDEAN INCREASE IN DYE DENSITY WITH DYE PRODUCED FROM SAID COUPLER IN THEAREAS CORRESPONDING TO THE IMAGEWISE DISTRIBUTION OF SAID METALLICSILVER, THE IMPROVEMENT COMPRISING INCLUDING IN SAID AMPLIFIERCOMPOSITION A COMPOUND WHICH IS AN ALIALI METAL SALT OF A PERACID OR OFFERRICYANIDE.
 2. A process according to claim 1 wherein said amplifierbath contains a sufficient quantity of development restrainer to represssubstantially any further net silver development.
 3. A process accordingto claim 1 wherein said color-developing agent imbibed in saidphotographic element is an aromatic primary amino compound.
 4. A processaccording to claim 1 wherein said development of the imagewise-exposedsilver halide emulsion is carried out in a liquid which is substantiallyfree from cobalt (III) metal complex salts.
 5. A process according toclaim 1 wherein said amplifier bath is substantially free from silverhalide solvents or contains less than 30 percent by weight of the silverhalide solvent which would be necessary to fix a silver halide emulsion.6. A process according to claim 1 wherein the compound is potassiumpersulfate.
 7. A process according to claim 1 wherein said compound isadded to said amplifier to maintain the concentration ofcolor-developing agent below 0.5 g./l.
 8. A process according to claim 1wherein said photographic element is a multicolor photographic elementcomprising at least two color-providing layer units, each of whichcontains a silver halide emulsion having associated therewith aphotographic color coupler in at least a 40 percent stoichiometricexcess based on silver.
 9. A process according to claim 1 wherein saidphotographic element is a photographic element comprising at least oneimage dye-providing layer unit which contains a silver halide emulsionhaving associated therewith a water-insoluble image dye-providingcoupler dissolved in a coupler solvent wherein said coupler is presentin at least a 40 percent stoichiometric excess based on effectivesilver.
 10. A process according to claim 8 wherein each of saidcolor-providing layer units contains a silver halide emulsion at aconcentration of less than 30 mg. silver/ft.2.
 11. A process accordingto claim 1 wherein the halide concentration of all silver halideemulsions in said element is less than 3 mole percent iodide.
 12. Aprocess according to claim 2 wherein said development restrainer issubstantially free from ionic iodide groups and free mercapto groups.13. A process according to claim 2 wherein said development restraineris the combination of from about 0.01 to about 2 g./l. of abenzotriazole and from 2 g. to about 40 g./l. of an alkali metalbromide.
 14. A process according to claim 1 wherein said amplifier bathcontains from about 2 g. to about 40 g./l. of an alkali metal bromide.15. A process according to claim 1 wherein said cobalt(III) metalcomplex is a cobalt hexammine salt.
 16. A process according to claim 1wherein said amplifier contains at least 0.5 g./l. of a sulfitecompound.
 17. A process according to claim 1 wherein said compound is aperacid.